Note to anyone melanin-deficient: Don’t put wax or oil or shit in dreads it prevents felting (just as natural hair grease does). Doesn’t really matter if you have thick curly hair thus black folks do it because it’s a quick way to deal with frizz, if you have any other hair structure though you’ll end up with candles instead of dreads.
The method for whiteys also works for black folks, and that’s residue-free, silicone-free soap (ordinary shampoos contain silicones to replace grease and thus prevent felting), then mechanical treatment: Palm rolling, root tightening, as well as crocheting (with a crocheting needle if you have someone to do it for you, otherwise a large needle with a string loop). Never use a hair-dryer instead learn to headbang, make sure to actually let your dreads dry to the core (can take a whole day from not dripping to dry, depending on temperature/humidity). Once in a while a sour rinse (apple cider vinegar or citric acid) to flush out mineral residue, ending every wash with a cold rinse also helps, that has to do with how the little scales on hair react to temperature, cold closes them.
As to specific products: I use Frosch dish washing detergent because I trust them to not put nasty shit in it, if you don’t have access to it use specialised dread shampoo (or if you don’t fancy smelling like janitorial lemon). Hard soaps can work but they’re not always stellar when it comes to being residue-free, some are right-out atrocious. Dudu Osun generally isn’t, and generally worth the price. As to acid: Actually straight citric acid dissolved in water. The same stuff I use to clean, or put in food if in a pinch (it’s food-grade). String for the needle: The absolute best you can get or you’ll be tearing it all the time.